Optical finger navigation (OFN) modules or systems make use of optical physics to measure the degree of the relative motion, in both speed and magnitude, between a navigation device and the navigation/tracking surface. These OFN systems find their major application in pointing and finger tracking devices and are becoming increasingly common in data processing systems, such as cellular telephones, tablet computers, electronic readers, control pad/console in automobiles and portable entertainment or game systems for data input and/or cursor movement. OFN systems in general include optical navigation sensors (ONS), which generally include a light source to illuminate a tracking surface, such as a finger or stylus in contact with a surface of the OFN system, and an optical sensor, such as a charge-coupled device (CCD), complementary metal-oxide-semiconductor (CMOS) imaging array, or a photo-diode array, or a photo-detector array, to capture an image or signal in light reflected and/or scattered from the tracking surface. A tracking program implemented in a single or multiple processor(s) coupled to the sensor analyzes successive images or signals to determine displacement of the OFN system relative to the tracking surface.
One of the problems with existing OFN systems is that the ONS, in particular the optical sensors, may not differentiate between light reflected or scattered off a finger or stylus and environmental or ambient light. Strong and variable ambient light can cause spurious detected motions known as auto-movements or light-induced motion. Sunlight is a particular problem especially for OFN systems installed in vehicles, and manufacturers usually require that the OFN systems pass strict sunlight tests with specified range of light intensity conditions, test time, test angle, and orientations relative to sunlight.